(a) Field of the Invention
This invention relates to ultrathin unit layer films and built-up multilayer films comprising a heteroaromatic polymer comprising repeat units of the formula ##STR1## where R is aromatic, heteroaromatic, olefinic, acetylenic, or a mixture of these, where Ar is an aromatic nucleus, and where X is selected from the group consisting of NR', S, O, Se, and Te, where R' is H, aromatic, or aliphatic; said X being in ortho (X, N) pairs.
This invention relates to a process for the polycondensation synthesis of heteroaromatic polymers and the deposition onto selected substrates of said snythesized heteroaromatic polymers in the form of unit layers and built-up mulitlayers.
This invention relates to heteroaromatic polymer unit layer films and multilayer films possessing a heretofore unrealized degree of thinness.
(b) Definitions of Terms
By the phrase "unit layer" is meant the film or monolayer which is formed according to the teachings of this invention when a compound is spread onto an aqueous surface such that the thickness of the resulting layer is less than 50 nanometers or such that the surface area occupied per molecule is less than the cross sectional area of said molecule or which forms as a result of a subsequent reaction of said film. The phrase "unit layer" also applies to the above unit layer, which is on the subphase surface, after said unit layer is transferred onto a substrate. The thickness of a unit layer is less than 50 nanometers. If the molecules in the unit layer each span the thickness of said unit layer, than said unit layer can be called a "monolayer". The film which results from the one-by-one transfer of unit layers onto a substrate such that they become piled in a stack is called a "multilayer".
By the phrase "aldehyde monomer precursor" is meant a compound which is capable of generating an aldehyde monomer when spread onto an appropriate aqueous subphase according to the teachings of this invention.
(c) Description of the Prior Art
While heteroaromatic polymers, including those described in this patent specification, and films made therefrom are known to the art, uniform, well-controlled films of less than 0.1 micrometers in thickness cannot be made by previously known methods.
Melt phase, solid-state, and solution phase syntheses of heteroaromatic polymers are known to the art. Recent reviews of this art are those of E. W. Neuse, Advances in Polymer Science, Vol. 47, pp. 1-42 (1982) and J. P. Critchley, Die Angewandte Makromoleculare Chemie, Vol. 108/110, pp. 41-80 (1982). Representative references of the prior art in the synthesis of heteroaromatic polymers are Y. Iwakura, K. Uno, Y. Imai, Journal of Polymer Science: Part A. Vol. 2, pp. 2605-2615 (1964), J. Higgins, C. S. Marvel, Journal of Polymer Science: Part A-1, Vol. 8, pp. 171-177 (1970), H. Vogel, C. S. Marvel, Journal of Polymer Science, Vol. L, pp. 511-539 (1961), H. Vogel, C. S. Marvel, Journal of Polymer Science: Part A, Vol. 1, pp. 1531-1541 (1963), J. F. Wolfe, F. E. Arnold, Macromolecules, Vol. 14. pp. 909-915 (1981), J. F. Wolfe, B. H. Loo, F. E. Arnold, Macromolecules, Vol. 14, pp. 915-920 (1981), R. C. Evers, F. E. Arnold, T. E. Helminiak, Macromolecules, Vol. 14. pp. 925-930 (1981), and E. W. Neuse, M. S. Loonat, Macromolecules, Vol. 16, pp. 128-136 (1983). Heteroaromatic polymers are characterized by high melting point and low solubilities. Because of these properties, ultrathin films of heteroaromatic polymers have been heretofore unobtainable.
Also, while ultrathin unit layers and monolayer ploymer films are known to the art, heretofore, not only have these been limited to polymers not possessing, in the main chain, the heteroaromatic moieties which are objects of this invention, but also they have been limited to polymers soluble in spreading solvents or which possess pendant long alkyl side chains. The following references are considered representative of the prior art in the area of polymerized and multilayers: R. Ackermann, et al. Kolloid-Z, Z. Polym., Vol. 2249, 1118 (1971), A. Cemel, et al. J. Polym, Sci., Pt A-1, Vol. 10, 2061 (1972), M. Puterman, et al, Journal of Colloid and Interface Science, Vol. 47, 705 (1974), R. Ackermann, et al, Makromol, Chem., Vol. 175, 699 (1974), A. Dubault, et al, J. Solid Films, Vol. 68, 1 (1980), D. R. Day and H. Ringsdorf, Makromol. Chem., Vol. 1880, 1059 (1979), B. Tieke, V. Enkelmann, H. Kapp, G. Lieser, and G. Wegner in "Interfacial Synthesis, Vol. III, Recent Advances, "Marcel Dekker: New York, 1981, K. Fukuda, Y. Shibasaki, H. Nakahara, J. Macromol. Sci.,-Chem., Vol. A15, 999 (1981), and T. Folda, L. Gros, H. Ringsdorf, Makromol, Chem., Rapid Commun., Vol. 3, 167 (1982). These references all deal with the polymerization of long chain aliphatic amphiphiles containing polymerizable groups such as vinyl, acrylic, and diacetylene moieties. These polymerizations are addition polymerizations which proceed via a free radical mechanism. The product polymer films retain the aliphatic nature of the starting monomers.
The polymers films and the process for making them, which are objects of this invention, differ from the prior art in the following respects. (1) The films of this invention may be wholly aromatic. (2) While the spreadable monomers described in this specification may have aliphatic chains attached to them, according to the process of this invention, these chains are eliminated from the final product film. (3) The polymerization process which is an object of this invention is a condensation type polymerization.
In a previous patent specification (Japanese Patent Unexamined Publication No. 108633/1986, U.S. Pat. No. 4,681,799, this inventor disclosed ultrathin films or polymeric imines synthesized at the air/water interface. While the invention described in the present specification is not bound by any theory, the mechanism for producing the ultrathin heteroaromatic films disclosed in this specification is thought to proceed through an imine intermediate by means of oxidative cyclodehydrogenation to the object heteroaromatic polymer films. Research on small molecules (K. H. Grellamnn and E. Tauer, J. Am. Chem. Soc., 95, 3105 (1973)), found that an aromatic anil formed from an aldehyde and an aromatic amine will undergo oxidative cyclodehydrogenation when a suitable reactive group is ortho to the amine group of said aromatic amine. Anils in which said reactive group is NH.sub.2, OH, or SH will form imidazoles, oxazoles, or thiazoles, respectively. A similar mechanism is thought to occur in the reaction forming the polymer films which are the object of this invention.
As mentioned above, uniform ultrathin films comprising a heteroaromatic polymer were not heretofore obtained. Ultrathin films comprising a polymer which is not soluble in spreading solvents and which has no alkyl side chains were also not heretofore obtained.